1. Field of the Invention
The present invention relates to voltage regulators, and particularly to a linear voltage regulator for providing a regulated voltage to a load mounted on a motherboard.
2. General Background
Linear voltage regulators are widely used to supply power to electronic devices, such as to a load on a motherboard of a computer. Such linear voltage regulators are available in a wide variety of configurations for many different applications.
Referring to FIG. 3, a typical linear voltage regulator 1 includes a voltage regulator IC (Integrated Circuit) 10. The voltage regulator IC 10 includes an adjusting terminal 11, an input terminal 12, and an output terminal 13. The adjusting terminal 11 receives an adjusting voltage V1. The input terminal 12 receives an input voltage Vin, and is grounded via a first filter capacitor C1. The output terminal 13 provides an output voltage Vout to a load RL, and is grounded via a second filter capacitor C2. Two resistors R1 and R2 are connected to each other in series, between the output terminal 13 and ground. A node N between the resistors R1 and R2 provides the adjusting voltage V1 to the adjusting terminal 11.
An impedance of each of the resistors R1, R2 is adjustable. When the resistor R1 or the resistor R2 has an appropriate impedance, the output voltage Vout can be regulated at a required level.
However, in the voltage regulator IC 10, when the input voltage Vin is 3.3V and the output voltage Vout is 1.5V, a load current is less than 0.1 A. Therefore the linear voltage regulator 1 cannot provide a greater current to the load. Furthermore, in the voltage regulator IC 10, a difference between the input voltage Vin and the output voltage Vout is between 1.3V and 1.5V. Therefore when a 1.5V output voltage Vout is needed, the input voltage Vin must be between 2.8V (i.e., 1.5V+1.3V) and 3.0V (i.e., 1.5V+1.5V). Otherwise, the linear voltage regulator 1 will not run properly.
What is needed, therefore, is a linear voltage regulator which is able to provide a greater current to a load and have a wide range of input voltages.